1. Field of the Invention
The present invention relates to a formation method of a semiconductor film having a crystalline structure which is formed by a laser crystallization technique, and a manufacturing method of a semiconductor device including a thin film transistor provided with the semiconductor film, or the like. More specifically, the present invention relates to a manufacturing method of a semiconductor device including an n-channel thin film transistor and a p-channel thin film transistor.
2. Description of the Related Art
In recent years, a laser crystallization technique in which an amorphous semiconductor film formed over a glass substrate is irradiated with a laser beam to form a semiconductor film having a crystalline structure (hereinafter, referred to as a crystalline semiconductor film) has been widely researched, and a large number of suggestions have been made.
The reason why the crystalline semiconductor film is used is that the crystalline semiconductor film has higher mobility than an amorphous semiconductor film. As a result, for example, TFTs using the crystalline semiconductor film is used for an active matrix liquid crystal display device or organic EL (electroluminescence) display device, or the like in which, over one glass substrate, TFTs for a pixel portion, or TFTs for a pixel portion and TFTs for a driver circuit are formed.
As a crystallization method, other than laser crystallization, there are a thermal annealing method using an annealing furnace and a rapid thermal annealing (RTA) method. When the laser crystallization is used, heat is absorbed by only a semiconductor film and crystallization can be performed without increasing substrate temperature so much. Therefore, a substance such as glass or plastic which has a low melting point can be used as the substrate. As a result, a glass substrate which is inexpensive and is easily processed even in a large area can be used, thus, production efficiency can be drastically improved by the laser crystallization.
In laser crystallization, a continuous-wave laser beam or a pulsed laser beam with a repetition rate of greater than or equal to 10 MHz is formed into a linear beam spot and the semiconductor film is irradiated with the laser beam while being scanned to move a solid-liquid interface, whereby crystals in the semiconductor film can be grown laterally. This method makes it possible to form a crystalline semiconductor film provided with a very large crystal which has a crystal grain with a width of several μm and a length of several tens of μm (hereinafter, referred to as large grain crystals). When the large grain crystal is used in a channel formation region of a thin film transistor, few grain boundaries are formed in a moving direction of carriers, and thus electrical barrier against the carriers is decreased. As a result, a thin film transistor which has mobility of about several hundreds of cm2/Vs can be manufactured.
The mobility of electrons which are carriers in an n-type thin film transistor or holes which are carriers in a p-type thin film transistor depends on an orientation of crystals planes. The n-type thin film transistor can obtain the best performance when a channel formation region is formed of crystals in which crystal planes are oriented along {001}, and the p-type thin film transistor can obtain the best performance when a channel formation region is formed of crystals in which crystal planes are oriented along {211} or {101} (Patent Document 1: Japanese Published Patent Application No. 2002-246606).